This invention relates to a heating device, provided with a heating chamber for objects, bounded by at least one heat-transmission wall whose side which is remote from the heating chamber forms part of the boundary of a reservoir in which a heat transport medium is present which completes an evaporation/condensation cycle during operation, involving on the one hand evaporation by taking up heat originating from a heat source and, on the other hand, condensation on the heat-transmission wall while giving off heat thereto.
A heating device of the kind set forth is described in application Ser. No. 534,621 filed Dec. 19, 1974, now U.S. Pat. No. 3,943,964, which is a continuation of application Ser. No. 159,205 filed July 2, 1971, now abandoned. Liquid heat transport medium which evaporates from the wall to which heat is supplied moves in the vapour phase to the heat-transmission wall as a result of any locally prevailing lower vapour pressure due to a slightly lower local temperature. Subsequently, the vapour condenses on the heat-transmission wall while giving off heat thereto, the said heat being given off through the wall to the heating chamber for the benefit of one or more objects to be subjected to heat treatment. The condensate is returned by capillary forces, via a capillary structure, to the wall where heat is supplied and where it is evaporated again. It is alternatively possible that the condensate is returned exclusively by gravity, i.e. without a capillary structure being present.
The major advantage of this kind of heating device is that a fully isothermal heating chamber is obtained in a comparatively simple manner, which is of major practical importance particularly in ovens. The isothermal nature results from the fact that the most vapour always condenses at the area on the heat-transmission wall where the lowest vapour pressure prevails. A locally lower temperature, consequently, is immediately compensated for.
It often occurs in practice that a plurality of heating devices which are constructed as an oven, each device comprising only one heating chamber, are simultaneously used at the same operating temperature in a factory hall. An example in this respect is the simultaneous use of a plurality of tunnel ovens where one or more wires which are covered with a layer of lacquer are fed through each oven in a continuous process in order to bake the lacquer on the wire. Each oven then has its own heat source such as a burner, an electric heating wire, a high-frequency induction coil or similar.